Interference-free a.-c. switch



Nov. 1, 1966 w. s. COOPER 3,283,177

INTERFERENCE-FREE A.-C. SWITCH I Filed Sept. 2, 1964 2 Sheets-Sheet 1 Fig.l

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58 52 I00 uf I 54 56 I INVENTOR. WILLIAM S. COOPER BY M ATTORNEYS United States Patent 3,283,177 INTERFERENCE-FREE A.-C. SWITCH William S. Cooper, Sacramento, Calif., assignor to Aerojet-General Corporation, Azusa, Calif., a corporation of Ohio Filed Sept. 2, 1964, Ser. No. 393,830

7 Claims. (Cl. 307-885) This invention relates to solid state switching device circuits and more particularly to a control circuit incorporating silicon-controlled rectifier switching devices by which the turn-on and turn-off switching transients are eliminated to provide a switching action substantially free from radio-frequency interference.

Turning off or turning on the A.-C. supply to inductive, resistive, lamp circuit or other high current loads can result in destructive transient impulses when the amplitude of the rise, or fall, of the power at the load circuit or device is very great. In the past, such turn-0n or turn-off functions have been performed primarily by mechanical switches.

More recently, the development of the silicon-controlled rectifier (SCR) otters means whereby switching problems involving high currents may be overcome through the use of SCR switches. Some of these prior art switching means entailed massive mechanical structures. With the SCR switches, more compact and efiicient structures are possible. These more compact and therefore lighter structures are particularly desirable in airborne and space vehicle where every saving in weight of operational equip ments permits greater payloads and/ or reduces fuel requirements.

The silicon-controlled rectifier (SCR) is a four-layer semiconductor device of PNPN configuration having three junctionsP-N, N-P, and P-N. They are sometimes considered as a PNP and NPN transistor with each enjoying one of their junctions in common. The anode of the SCR is the P element of the first junction, and the cathode of the SCR is the N element of the third junction. In the SCR, a gate signal is applied to the P element of the second and third junction. When a potential is applied between anode and cathode with the positive polarity at the anode and negative polarity at the cathode, practically no current can flow since the center junction is reverse biased while the outer junctions are forward biased. There is a leakage current, I in the 01f condition which is very small. The total current in the external circuit is determined by the relationship:

where I =total current I =leakage current at the reverse-biased (central) unction a and a =current gains in forward-biased junctions considered as NPN or PNP transistors.

So long as a +a is equal to .9, the total current will be 10 times the leakage current. But since the leakage current, nc, can be made extremely small in a silicon PN junction, the total current will therefore be very small. This is the off condition of the SCR. When the current gains add up to nearly unity, the denominator of Equation 1 is almost zero and the total current, I, limited only by the load elements in the external circuit.

When a small forward biasing current is applied to the gate element, the current gain is increased until a voltage is reached at which an avalanche multiplication occurs and increases very rapidly until the total current is sufficient to maintain the sum a t-r1 51 at which point the SCR becomes highly conductive and behaves as a P-N rectifier. This condition of high conduction (the on condition) prevails so long as the total current through the SCR remains above a critical minimum current called the holding current. If the current through the SCR falls below this holding current, the SCR will abruptly revert to the forward blocked or off condition. The off condition is generally achieved, once conduction has started, by a reverse voltage applied to the SCR. Removing the gate current, once conduction has started, has no effect, and the SCR continues to conduct indefinitely until something in the external circuit reduces the current below the holding value.

The turn-on action described above, wherein a small forward biasing current is applied to the cathode P-N junction, is described as triggering or firing of the SCR. The process by which the forward current is reduced below the holding current is called commutation.

The rise-time on turn-on and fall-time on turn-off of an SCR is quite abrupt. The rise or fall in associated current is so rapid as to generate radio-frequency components which may be radiated to nearby circuits or coupled directly through power or other wiring.

In the prior art, suppression of the interfering radiation due to the rapid rise or fall of current on SCR turnon, or turn-off has been attempted by shielding the unit containing SCR elements. In some cases radio-frequency blocking filters have been employed in the power line. One direct approach to eliminating the RF transient, which has been applied to the SCR circuit itself, has been to incorporate an appropriate series inductance in the SCR anode lead and an appropriate capacitor across both the inductance and SCR. The latter approach tends to impede the rate of rise in current.

The present invention contemplates novel circuit means associated with SCR switch devices with which A.C. power can be applied to and removed from various high current load equipments while substantially reducing or eliminating conducted or radiated radio-frequency (RF) interference caused by turn-on or turn-01f transients.

In the present invention, two silicon controlled rectifiers are arranged in parallel but with opposite polarities across an A.C. switching circuit. Accurate control is maintained of the point with respect to the A.C. line voltage at which the SCR will be gated on. The two SCRS are designated Positive SCR and Negative SCR.

Control of the gating point is accomplished by charging a gate voltage source capacitor for the positive SCR only during the negative half-cycle of the alternating current (A.C.) sine wave and charging a gate-voltage source capacitor for the negative SCR during the positive half cycle of the A.C. sine wave. As a result, after a turn-on command signal, the conduction of each SCR is delayed until at least the next half-cycle. That is, each SCR will not turn on until immediately after the A.C. signal has passed through zero, and after the charging of the gate control voltage capacitor connected to it which has been charged by the previous half-cycle of opposite polarity. Thus A.C. power turn-on only occurs very close to the zero cross-over point of the A.C. sine wave half-cycle and so the rise or fall at turn-on will amount to a negligibly small amplitude and produce no radio-frequency interference type of radiation.

It is accordingly an object of this invention to provide an A.C. switching circuit substantially free of radio-frequency interference.

It is another object of this invention to provide a silicon controlled rectifier on-otf control circuit for inductive, resistive and other loads which is substantially free from undesired radiation due to sharp transients.

i2 It is still another object of this invention to provide means for gating SCR elements on and off by providing means which insures that the rise and fall times of the a command signal is applied to a step-down transformer having inverting dual secondaries, each secondary being arranged to develop and store a positive-going gate pulse to an SCR switching device on thepre-ceding out-of-phase half-cycle of the A.C. sine-wave signal being applied to the switching device, the SCR being responsive to the gate signal only during the half-cycle following the development of the gate pulse.

It is a still further object of this invention to provide first and second gate-pulse charge and storage means responsive to respective and successive alternate half-cycles of an A.C. and connected to respective parallel oppositely poled SCR elements in series with an A.C. load, each said SCR being so poled as to respond to the gate pulses only during the half-cycle next following that in which the associated gate-pulse charge storage circuit therefor has achieved a potential suflicient to fire that SCR.

These and other objects of this invention will be more clearly evident from the specification which follows and the appended claims taken together with the accompanying drawings in which:

FIGURE 1 is a schematic circuit diagram of the interference-free switching system of this invention; and

' FIGURES 2a and 2b are waveform charts showing the time relationship of the signals involved in the operation of the invention.

In FIGURE 1, an A.C. power source A-B is seen to be connected to input terminals 2 and 6 of .a switching control circuit in accordance with this invention. The circuit 10 is enclosed in a broken line outline. Arcoss the input 2-6, the primary 14 of a transformer 12 is connected in series with a single-pole single-throw switch 8, shown in an open circuit condition. A terminal 4 of transformer primary 14 is connected to the arm 7 of switch 8. The contact terminal 9 of switch 8 is connected to source input'terminal 2. The other terminal 5 of transformer primary 14 is connected to source input terminal 6.

Transformer 12 has two secondary windings 1-6 and 18 on a common core but each independent of the other and each poled so as to provide a signal inverted in phase with respect to the other primary. This is shown by the location of dots 3 on primary and secondaries 16 and 18 and the polarity identifications thereat. When the dot 3 (input terminal 4) side of primary winding 14 is positive with respect to terminal 5 then terminal 16a is positive with respect to terminal 16b of secondary winding 16 and terminal 18a is positive with respect to terminal 18b of secondary winding 18.

The principal purpose of transformer 12 is to provide a pair of independent and phase-opposed signals to be used as hereinafter described. The phase-opposed signals may be rectified to produce appropriate gating signals for the SCRs.

In place of transformer 12 various other means for providing phase-opposed independent output signals may be used by those skilled in this art. An example of such other means is a common-emitter transistor phase-inverter in which the independent outputs are derived, respectively, from collector and emitter-circuits and the input to the base thereof from a voltage divider network across the A.C. line.

Unijunction transistors may also be used in appropriate circuit configurations to derive therefrom independent phase-opposed output signals.

Across secondary winding 18, a half-wave rectifier circuit is connected including a current-limiting and timing resistor 20 connected to the dot 3 terminal at 18a, a diode 22 connected in series with resistor 20 to the positive terminal of a charging and storage capacitor 28. The negative terminal of capacitor 28 is connected to terminal 18b of transformer secondary 18 and A.C. power source input terminal 2. A load resistor 30 is connected in parallel with capacitor 28.

Across secondary Winding 16 of transformer. 12, a similar half-wave rectifier circuit is connected in which a current limiting and timing resistor 50 is connected to non-dot terminal 16b of winding 16, a diode 52 is connected in series with resistor 50 to the positive terminal of a charging and storage capacitor 58. A load resistor 60 is connected in parallel with capacitor 58. The negative terminal of capacitor 58 is connected to terminal 16a of winding 16. Terminal 16a is also connected to switched ends 76 of the load circuit 79. The common end 7 of load circuit 79 is at 78 connected to common terminal side.

6 of the input circuit.

A capacitor 46 is connected between input terminal 2 and load terminal 76. Capacitor 46 is thus in parallel with the SCRs 38 and 68 to suppress internally generated transients.

A first silicon controlled rectifier (SCR) 38 is connected between terminal 2 and terminal 76 with the cathode 42 thereof connected to terminal 2 and the anode 48 thereof to terminal 76.

The gate terminal 44 of the SCR 38 is connected through a coupling diode 32 to the positive terminal of capacitor 28. Coupling diode 32 is poled so that the anode 34 is connected to the positive terminal of capacitor 28 and the cathode36 is connected to gate terminal 44. Thus only when the potential on the anode 34 of diode 32 is positive with respect to the cathode 36 will there be any transfer of gate signal to gate terminal .44.

A second SCR 68 is also connected between input terminal 2 and load terminal 76, but SCR 68 is oppositely poled with respect to SCR 38. The anode 70 of SCR 68 is connected to terminal 2. The gate terminal 74 of SCR 68 is connected through coupling diode 62 to the positive terminal of capacitor 58. Coupling diode 62 is poled so that anode 64 thereof is connected to capacitor 58 and cathode 66 thereof is connected to gate terminal 74. Thus, only when the potential of anode 64 is positive with respect to cathode 66 of diode 62 will there be any transfer of gate signal to gate terminal 74.

From. the above, it may be seen that the control circuit comprises an A.C. source circuit A-B connected to input terminals 2, 6 of the control circuit 10 of this invention. The output or load 79 is connected to terminals 76, 78. The terminals 78 and 6 are common. Between terminal 2 and terminal 76, the switching circuit comprising SCRs 38 and 68 is connected along with the associated gating control circuits for each. The parallel connected but 0p-- positely poled SCRs 38 and 68 are in series with terminals 2 and 76.

The gating control circuits comprise the respective rectifier networks connected to the secondary windings 16 and 13 of transformer 12 and coupled respectively to gate terminals 74 and 44 of SCRs 68 and 38, respectively.

The operation of the system shown in FIGURE 1 and described in detail above will be better understood in the following discussion thereof with reference to both FIG-' URES 1 and 2. In FIGURE 2, waveforms of the currents or signals involved with respect to time have been drawn to aid in the discussion.

FIGURE 2 is illustrated in two related parts side-by- At the left (FIG. 2a) the waveforms of signal present during the turn-on phase of operation of the invention are shown, and at right (FIG. 2b) the waveforms related to turn-off phase of operation are shown.

In opera-ting the invention, switch 8 (FIG. 1) is actuated by closing arm 7 against contact 9 to complete the circuit from terminal A to terminal B across the primary 14 of transformer 12 applying the power line A.C. current across primary 14 at time t as indicated at 80 in FIGURE 2a.

For the ensuing discussion, it is assumed that the AC. current at 80 (FIG. 2a) applied to primary 14 is of positive polarity at terminal 4 and negative polarity at terminal 5 so that there is induced on secondaries 16 and 18 a stepped-down A.C. signal with the polarities inverted with respect to the primary polarity as shown at 16a, 16b, and 18a, 18b. The corresponding waveforms are shown at 82 and 84 respectively in FIGURE 2a. Thus the anode 54 of diode 52 will have a negative polarity with respect to return line 76a, and anode 24 of diode 22 will have a positive polarity with respect to return line 2a.

Diode 22 therefore will conduct on the initial rise of current which charges capacitor 28 in the manner shown in waveform 86 in FIGURE 2a; The time constant of the RC discharge path represented by capacitor 28 and resistor 38 in parallel therewith is very long compared to the period of the alternation cycle of the A.C. signal applied to diode 22 so that the charge remains on diode 22 over the next cyclic alternation interval, and by virtue of the half-wave rectification action of diode 22, capacitor 28 will retain a charge relatively constant until AC. power is removed from winding 14 and therefore also from winding 18. During this initial half cycle 81 or the portion thereof during which power is applied, there is no conduction of the AC. potential applied between terminals 2 and 6 across SCRs 38 and 68 to load 79. This is shown at 88 in FIGURE 2a.

During the next (negative) half-cycle 89 of the primary power applied to primary 14, the polarity of the potential appearing on secondaries 16 and 18 is inverted so that the non-dot ends (16b of winding 16, and 18b of winding 18) are now positive resulting in non-conduction of diode 22 and conduction of diode 52 in the same manner as diode 22 was conducting on the preceding half-cycle. Capacitor 58 is now charged up as can be seen at 90 in FIG- URE 2a. Capacitor 58 and resistor 60 are similar to capacitor and resistor 28 and 30 in that capacitor 58 retains its charge over the alternate successive half-cycles of AC. potential in winding 16.

As has been previously explained, an SCR remains non-conductive until an appropriate forward gating potential is applied to the gating terminal thereof. Thus, during a negative half-cycle (with respect to the direction in which the SCR is poled) no conduction occurs. When a coincidence of forward bias and forward gating potential are present on the SCR, the SCR acts like a diode and conducts during the half-cycle in which the coincidence occurs.

Accordingly, during the later half of half-cycle 81 (FIG. 2a) at the peak of which power has been applied, as indicated at 88, to primary 14, neither SCR 38 nor 68 becomes conducting (as indicated at 88) because the polarity of the potential on anode 70 of SCR 68 is positive with respect to cathode 72 thereof, and capacitor 58 has no charge upon it because diode 52 is non-conducting during this half-cycle. The polarity of potential applied to cathode 42 of SCR 38 is positive with respect to anode 40 so that even with the forward-bias between cathode 42 and gate terminal 44 developed across RC network 28, 30, SCR 38 is not conducting because the SCR is itself reverse-biased.

During the next full positive half-cycle 94 of the AC. source A-B applied to the terminals 2-6, SCR 68'now has a positive potential on the anode 70 thereof with respect to the cathode 72 thereof, and there is a forward gating signal applied to gate terminal 74 across coupling diode 62 from capacitor 58 and SCR 68 now conducts on the positive ha1f-cycle of AC. power from source A-B applied to terminals 2 and 6 to load 79 across terminals 76 and 78 as shown at 98 in FIGURE 2a.

The rise in conduction of SCRs 38 and 68 on the respective succeeding half-cycles, after a gate potential has been developed on respective capacitors 28 and 58,

can only start at a time I or t in the cycle after the zero crossovers, as indicated at in FIGURE 2a, because of the configuration of this circuit, thereby eliminating the sharp transient which otherwise would have accompanied the sharp turn-on rise occurring at t indicated at 82 and 84 in FIGURE 2a.

Similarly as may be seen in FIGURE 2b on turn-off, following a conduction cycle 102 for SCR 68, on the succeeding positive-half-cycle, during which the conduction of SCR 38 occurs, if A.C. power is now removed by opening switch 8, as indicated at 106 and 108, the resulting drop in potential terminates the successive charging of capacitors 28 and 58. Both capacitors 28 and 58 discharge through their respective load resistors 30 and 68 over a time period which may be greater than the succeeding /2 cycle as indicated at 109 and which will depend on the value of resistors 30 and 60. If resistors 30 and 60 are relatively large the discharge may continue for more than one cycle. As has been previously explained, once an SCR has been fired or triggered by an appropriate gating signal, removing the gating signal does not terminate its conduction. Thus, until capacitors 28 and 58 have discharged below the firing potential for SCRs 38 and 68, the SCRs will continue to conduct. Then, on the half-cycle next following the fall of gate potential below the firing or holding potential value, conduction of the respective SCRs 38 and 68 will cease as the last half-cycle during which the gate signal for each SCR was present crosses the zero potential line of the AC. current source, as shown at 110, thereby eliminating the sudden drop in potential at turnoff.

Since the rise and fall in current applied to the load through SCRs 38 and 68 follows the AC. waveform, no sharp transition in turn-on or turn-off of the SCRs occurs. Therefore, when using the above described invention, no switching transients are developed of such nature that radio-frequency interference is generated.

What I claim is:

1. A silicon-controlled gated rectifier switching system comprising:

a source of alternating current having at least a current lead, and a common lead;

a first gated silicon-controlled rectifier means connected in series with said current lead and poled so as to be conductive, only during the concidence of a first forward-biasing gating signal and the positive half-cycles of the alternating current in said source;

a second gated silicon-controlled rectifier means connected in parallel with said first gated silicon-controlled rectifier means and poled so as to be conductive only during the coincidence of second forwardbiasing gating signal and the negative half-cycles of the alternating current in said source; 7

phase-inverting means coupled to said source for developing alternating-current signals which are opposite in phase with respect to said source;

first forward-biasing-signal generating means connected to said phase inverting means in such polarity as to produce a first positive direct-current gating potential on the half-cycle of the alternating current in said phase-inverting means corresponding to negative halfcycles of said source, said first forward-biasing signal generating means being connected to said first gated silicon-controlled rectifier;

second forward-biasing-signal generating means connected to said phase-inverting means in such polarity as to produce a second positive direct-current gating potential on the half-cycle of the alternating cur rent in said phase-inverting means corresponding to the positive half-cycle in said source, said second forward-biasing-sig-nal generating means being connected to said second gated silicon-controlled rectifier; and,

a load device being connected between said parallel connection of said silicon-controlled rectifiers and said common lead of said alternating-current source, whereby when alternating current from said source series with said current lead and poled so as to be conductive during the coincidence of a first forward- 55 in said second charge-storage means, said second rectifier-circuit means being connected to said second gated silicon-controlled rectifier; and a load device being connected between said parallel is applied to said phase-inverting means said first connection of said silicon-controlled rectifiers and gating potential is applied to said first gated siliconsaid common lead of said alternating-current source, controlled rectifier which does not conduct until whereby when alternating current from said source is there is coincidence of said first gating potential with applied to said phase-inverting means, said first gata succeeding positive half cycle of said source ing potential is applied to said first gated silicon-conwhereupon conduction of said first .silicon-con- 10 trolled rectifier during a negative half-cycle of said trolled rectifier occurs beginning at the initiation of alternating-current source and remains thereon due said succeeding positive half-cycle of said source to said first charge-storage means until the coinciand on succeeding positive half-cycles thereafter, and dence of the next positive half-cycle, and said first said second gating potential is applied to said second gating potential on said first silicon-controlled recgated silicon-controlled rectifier which does not contifier occurs to cause said first silicon-controlled recduct until there is coincidence of said second gating tifier to conduct on each following positive half-cycle potential with a next-following negative half-cycle of of said source thereafter, and said second gating posaid alternating-current source whereupon conduction tential is applied to said second gated silicon-conof said second silicon-controlled rectifier occurs betrolled rectifier to remain thereon due to said second ginning at the initiation of said next-following negacharge-storage means until the coincidence of the tive *half-cycle of said alternating-current sou-Ice next negative half-cycle, and said second gating p0- and on negative half-cycles of said source following tential on said second silicon-controlled rectifier octhereafter, so that alternating current from said ours to cause said second silicon-controlled rectifier source may be applied to said load, and when said to conduct on said next-following negative halfalternating current from said source is removed from cycle and on each following negative half-cycle of said phase-inverting means said first silicon-consaid source thereafter, so that alternating current trolled rectifier will no longer conduct at the befrom said source may be applied to said load, and ginning of the first negative half-cycle thereafter, at when said alternating current from said source is which said coincidence is not present, and said secremoved from said phase-inverting means both said end silicon-controlled \rectifier will no longer concharge-storage means will discharge and said first duct at the beginning of the first positive half-cycle silicon-controlled rectifier will cease conduction at thereafter, at which said coincidence is not present, the beginning of the first negative half-cycle at which thereby removing said alternating current from said said first charge-storage means is discharged below load, said application of said alternating current I a predetermined potential and said second siliconthereby to said load occurring on the rise of a posicontrolled rectifier will cease conduction at the betive or negative half-cycle without sudden change ginning of the first positive half-cycle at which said and the removal of said alternating current from said second charge-storage means is discharged below load occurring on the fall of a half-cycle without said predetermined potential thereby removing said sudden change, so as to eliminate high-frequency alternating current from said load, said application interference producing transients. 40 of said alternating current thereby to said load occur- 2. A silicon-controlled gated rectifier switching sysring on the rise of a positive or negative half-cycle tem comprising: without sudden change and the removal of said a source of alternating current having a current lead, al ernating current from said load occurring on the and a common lead; fall of a half-cycle without sudden change, so as to a first gated silicon-controlled rectifier connected in eliminate high-frequency interference producing transients. 3. An interference-free silicon-controlled gated-rectifier switching system for applying alternating current to a load and removing said current from said load, said system comprising:

biasing gating signal and the positive half-cycles of the alternating current in said source;

a second gated silicon-controlled rectifier connected in parallel with said first gated silicon-controlled recti fier and poled so as to be conductive during the coincidence of a second forward-biasing gating signal and the negative half-cycles of the alternating cura source of alternating current having at least a current lead and a common lead; a first gated silicon-controlled rectifier connected in series with said current lead and poled so as to be rent in said source; conductive, when gated, only on the positive halfphase-inverting means coupled with said source for decycles of the alternating current in said source;

Veloping alternating-current i n l whi h ar o a second gated silicon-controlled rectifier connected in posite in phase with respect to said source; parallel with said first gated silicon-controlled rectifier first rectifier-circuit means including first charge-storage and poled So as be Conductive When gated, only means connected to said phase-inverting means in 011 negative half-Cycles 0f the alternating Current such polarity as to produce a first positive direct n Said Source; current gating potential on the half-cycle 0f th alternating-current signal-inverting means for developalternating current in said phase inverting means corg P pp alternating-Current Signals 60inre onding to the concurrent negative half-cycle f cident but out-of-phase with said alternating current said source, said first gating potential being stored in in id Source; said charge-storage means, said first rectifier-circuit an OII-Off Switch intereonneetiflg the Signal-inverting means being connected to said first gated silicon-conmeans and the Source Of alternating Current; tr lled ectifier; a first gating-signal-circuit means having a first storage second rectifier-circuit means including second chargenetwork therein and being responsive to a predeterstorage means connected to said phase-inverting milled P y 0f Said P -Opposed alternating-curmeans in such polarity as to produce a second positive Tent signals to Produce a first Positive direct Current direct-current gating potential on the half-cycle of gating potential on the half-cycle of the alternating the AC. current in said phase-inverting'means corcurrent in said signal-inverting means corresponding responding to the concurrent positive half-cycle in to the concurrent negative half-cycle in said source, said source, said second gating potential being stored said first gating potential being stored in said storage network, said first gating-signal-circuit means being connected to said first gated silicon-controlled rectifier;

second gating-signal-circuit means having a second 10 lead of said source through an on-otf switch to said current lead of said source; a first half-wave rectifier circuit including a first diode and first charge-storage network connected to one of storage network therein and being responsive to the said secondary windings in such polarity as to produce opposite polarity of said phase-opposed alternatinga first positive direct-current gating potential on the current signals to produce a second positive directhalf-cycle of the current in said one secondary corcurrent gating potential on the half-cycle of the responding to the concurrent negative half-cycle in alternating current in said signal-inverting means corsaid primary winding, said first gating potential beresponding to the concurrent positive half-cycle in ing stored in said first charge-storage network, said said source, said second gating potential being stored first half-wave rectifier circuit being connected to said in said second storage network, said second gatingfirst gated silicon-controlled rectifier; signal-circuit means being connected to said second a second half-wave rectifier circuit including a second gated ili o ontrolled re tifier; and diode and second charge-storage network connected load device being connected between said parallel to the other of said secondary windings in such polarconnection of said silicon-controlled rectifiers and ity as to produce a second positive direct-current said common lead of said alternating-current source, gating potential on the half-cycle of the alternating whereby when alternating current is applied to said current in said other secondary corresponding to the signal-inverting means said first gating potential is concurrent positive half-cycle in said primary windapplied to said first gated silicon-controlled rectifier ing, said second gating potential being stored in said during a negative half-cycle of said alternating-cursecond charge-storage network, said second half-wave rent source to remain thereon due to said first storage rectifier circuit being connected to said second gated network until the succeeding positive half-cycle, silicon-controlled rectifier; and whereupon conduction of said first gated silicona load device being connected between said parallelcontrolled rectifier occurs beginning at the initiation connected silicon-controlled rectifiers and said comof said succeeding positive half-cycle and on each mon lead of said alternating current source, succeeding positive half-cycle thereafter, and said whereby when said on-off switch in said primary windsecond gating potential developed during said sucing is closed and alternating current thereby applied ceeding positive half-cycle of said alternating-current to said primary winding, said first gating potential source will be applied to said second gated siliconwill be applied to said first gated silicon-controlled controlled rectifier to remain thereon until the nextrectifier during a negative half-cycle of said alternatfollowing negative half-cycle of said alternating curing current source and remain thereon due to the rent source due to said second storage network where charge on said first storage network until the sucupon conduction of said second silicon-controlled ceeding positive half-cycle whereupon conduction of rectifier occurs beginning at the initiation of said said first silicon-controlled rectifier occurs beginning next-following negative half-cycle of said alternating at the initiation of said succeeding positive half-cycle current source and each following negative half-cycle and on each positive half-cycle following thereafter, of said source thereafter, so that alternating current and said second gating potential developed during from said source may be applied to said load, and said succeeding positive half-cycle of said alternating when said on-olf switch is open to remove said current source will be applied to said second gated alternating current from said signal-inverting means, silicon-controlled rectifier to remain thereon until the both said storage networks will discharge and said next following negative half-cycle of said alternating first silicon-controlled rectifier will cease conduction current source due to said second storage network at the beginning of the first positive half-cycle at whereupon conduction of said second silicon-conwhich said second storage network is discharged betrolled rectifier occurs beginning at the initiation of low said predetermined potential thereby removing said next-following negative half-cycle of said altersaid alternating current from said load, said applicanating current source and each negative half-cycle tion of said alternating current thereby to said load of said source following thereafter, so that alternating occurring on the rise of a positive or negative halfcurrent from said source may be applied to said load, cycle without sudden change and the removal of said and when said on-oif switch is open to remove said alternating current from said load occurring on the alternating current from said primary winding, both fall of a half-cycle without sudden change, so as to said storage networks will discharge and said first eliminate high-frequency interference producing silicon-controlled rectifier will cease conduction at the transients. beginning of the first negative half-cycle at which 4. A silicon-controlled gated-rectifier switching system said first storage network is discharged below a preo ri i determined potential and said second silicon-cona source of alternating current having at least a current trolled rectifier will cease conduction at the beginning lead, and a Gammon lead; of the first positive half-cycle at which said second a first gated silicon-controlled rectifier connected in stQmge HetWQTk 1S dlschal'ged b e10W p t series with said current lead and poled so as to be mmed POtentlal Phereby renfowng alternatlQg conductive, only on the positive half-cycles of the current from sa1d load sa1d ,apphcatlon sa1d alternating current in said source when a forwardaltenifitmg current thereb y to sa1d load.occumng on in atin Si a1 is also resent thereom the rising slope of a positive or negative half-cycle 1 s g g g p without sudden change and the removal of sa1d altera second gaied lcondcontroniq rectlfier connect; m nating current from said load occurring on the fallparallel with sa1d first gated sllrcon-c ontrolled rectifier ing Slaps {of a half cycle Without Sudden change, so and poled so as to be Conductlve only P the negatlve as to eliminate high-frequency interference producing half-cycles of the alternating current in said source transients Wh a forward-biasing gatlng slgnal is also Present 5. An interference-free switching system for switching thereon} 7 an alternating current source on and off as applied to a transformer having a primary winding and a pair of secondary windings, both said secondary windings developing alternating current from said source which is opposite in phase with respect to said source, said primary winding being connected from said common alternating current loads, particularly loads which are in or near interference sensitive devices, said switching system comprising:

gated switching means connected in series with one leg of the alternating current source and being responsive 1 l to predetermined gating signals to become conductive on successive alternate half-cycles;

a load circuit connected between said gated switching means and another leg of said alternating current source; and

dual gate-signal-generating means switchably connected to said source of alternating current for generating independent predetermined gating signals on either halficycle of the current in said alternating current source, said gate-signal-generating means being connected to said gated switching means to apply said independent predetermined gating signals to said gated switching means on said successive alternate half-cycles of said source without developing transients therein when applying said alternating current to said load in response to said signals, or removing said alternating current from said load when said signals are terminated, said load being thereby switched on or off without generating or radiating interference signals.

6. An interference-free switching system for switching a single-phase alternating current source on and oil as applied to alternating current loads, particularly loads which are in or near interference-sensitive devices; said switching system comprising:

a pair of gated-switching means connected in series with one leg of the alternating current source and each of said switching means being respectively responsive to predetermined gating signals to become conductive;

a load circuit connected between said gated switching means and the other leg of said alternating current source; and

a pair of gate-signal-generating means switchably connected to said source of alternating current, for generating independent, predetermined gating signals on either half-cycle of the current in said alternating current source, said gate-signal-generating means being connected to respective ones of said gated'switching means to apply appropriate ones of said independent predetermined gating signals to said gated switch-,

first and second gated-switching means connected in 'a load circuit connected between said parallel connected gated switching means and the other leg of said alternating current source; and

dual gate-signal-generating means switchably connected to said source of alternating current and including first and second gate potential circuits for generating and storing independent, predetermined gating signals during the half-cycle of the current in said alternating current source when each of said respective first and second gated switching means is nonconductive, said first and second gate potential circuits being connected to said gated switching means so as to apply said stored, independent, predetermined gating signals to said respective first and second gated switching means on the succeeding alternative half-cycle when each said respective switching means is conductive to apply said alternating current to said load circuit, said alternating current being applied to said load circuit only during the simultaneous presence of said respective gating signals and the conductive half-cycles of said respective first and second gated switching means, whereby current to said loads follows the rise and fall of the waveform of said alternating current in said source so that no abrupt application'to, or rem-oval of current from, said load occurs, thereby eliminating transients and high-frequency interference resulting therefrom.

References Cited by the Examiner UNITED STATES PATENTS ing means on alternate half-cycles of said source with- 2 169 8/1939 Dawson 315 197 X out developing transients therein to gate said gated 2516422 7/1950 Rockafenlow 328 77 switching means on so as to apply said alternating 3:097:314 7/1963 Harriman 3O7 88'5 i Sald load- 3,103,618 9/1963 slam.

7. An interference-free switching system for switching 3 159 753 12/1964 Anderson et a1 307 88 5 a single-phase alternating current source on and off as :2 8/1965 Snygg applied to alternating current loads, particularly loads which are in or near interference-sensitive devices; said switching system comprising:

ARTHUR GAUSS, Primary Examiner.

R. H. EPSTEIN, I. C. EDELL, Assistant Examiners. 

1. A SILICON-CONTROLLED GATED RECTIFIER SWITCHING SYSTEM COMPRISING: A SOURCE OF ALTERNATING CURRENT HAVING AT LEAST A CURRENT LEAD, AND A COMMON LEAD; A FIRST GATED SILICON-CONTROLLED RECTIFIER MEANS CONNECTED IN SERIES WITH SAID CURRENT LEAD AND POLED SO AS TO BE CONDUCTIVE, ONLY DURING THE CONCIDENCE OF A FIRST FORWARD-BIASING GATING SIGNAL AND THE POSITIVE HALF-CYCLES OF THE ALTERNATING CURRENT IN SAID SOURCE; A SECOND GATED SILICON-CONTROLLED RECTIFIER MEANS CONNECTED IN PARALLEL WITH SAID FIRST GATED SILICON-CONTROLLED RECTIFIER MEANS AND POLED SO AS TO BE CONDUCTIVE ONLY DURING THE COINCIDENCE OF SECOND FORWARDBIASING GATING SIGNAL AND THE NEGATIVE HALF-CYCLES OF THE ALTERNATING CURRENT IN SAID SOURCE; PHASE-INVERTING MEANS COUPLED TO SAID SOURCE FOR DEVELOPING ALTERNATING-CURRENT SIGNALS WHICH ARE OPPOSITE IN PHASE WITH RESPECT TO SAID SOURCE; FIRST FORWARD-BIASING-SIGNAL GENERATING MEANS CONNECTED TO SAID PHASE INVERTING MEANS IN SUCH POLARITY AS TO PRODUCE A FIRST POSITIVE DIRECT-CURRENT GATING POTENTIAL ON THE HALF-CYCLE OF THE ALTERNATING CURRENT IN SAID PHASE-INVERTING MEANS CORESPONDING TO NEGATIVE HALFCYCLES OF SAID SOURCE, SAID FIRT FORWARD-BIASING SIGNAL GENERATING MEANS BEING CONNECTED TO SAID FIRST GATED SILICON-CONTROLLED RECTIFIER; SECOND FORWARD-BIASING-SIGNAL GENERATING MEANS CONNECTED TO SAID PHASE-INVERTING MENS IN SUCH POLARITY AS TO PRODUCE A SECOND POSITIVE DIRECT-CURRENT GATING POTENTIAL ON A HALF-CYCLE OF THE ALTERNATING CURRENT IN SAID PHASE-INVERTING MEANS CORRESPONDING TO THE POSITIVE HALF-CYCLE IN SAID SOURCE, SAID SECOND FORWARD-BIASING-SIGNAL GENERATING MEANS BEING CONNECTED TO SAID SECOND GATED SILICON-CONTROLLED RECTIFIER; AND, A LOAD DEVICE BEING CONNECTED BETWEEN SAID PARALLEL CONNECTION OF SAID SILICON-CONTROLLED RECTIFIERS AND SAID COMMON LEAD OF SAID ALTERNATING-CURRENT SOURCE, WHEREBY WHEN ALTERNATING CURRENT FROM SAID SOURCE IS APPLIED TO SAID PHASE-INVERTING MEANS SAID FIRST GATING POTENTIAL IS APPLIED TO SAID FIRST GATED SILICONCONTROLLED RECTIFIER WHICH DOES NOT CONDUCT UNTIL CONTROLLED RECTIFIER WHICH DOES NOT CONDUCT UNTIL A SUCCEEDING POSITIVE HALF CYCLE OF SAID SOURCE WHEREUPON CONDUCTION OF SAID FIRST SILICON-CONTROLLED RECTIFIER OCCURS BEGINNING AT THE INITIATION OF SAID SUCCEEDING POSITIVE HALF-CYCLE OF SAID SOURCE AND ON SUCCEEDING POSITIVE HALF-CYCLES THEREAFTER, AND SAID SECOND GATING POTENTIAL IS APPLIED TO SAID SECOND GATED SILICON-CONTROLLED RECTIFIER WHICH DOES NOT CONDUCT UNTIL THERE IS COINCIDENCE OF SAID SECOND GATING POTENTIAL WITH A NEXT-FOLLOWING NEGATIVE HALF-CYCLE OF SAID ALTERNATING-CURRENT SOURCE WHEREUPON CONDUCTION OF SAID SECOND SILICON-CONTROLLED RECTIFIER OCCURS BEGINNING AT THE INITIATION OF SAID NEXT-FOLLOWING NEGATIVE HALF-CYCLE OF SAID ALTERNATING-CURRENT SOURCE AND ON NEGATIVE HALF-CYCLES OF SAID SOURCE FOLLOWING THEREAFTER, SO THAT ALTERNATING CURRENT FROM SAID SOURCE MAY BE APPLIED TO SAID LOAD, AND WHEN SAID ALTERNATING CURRENT FROM SAID SOURCE IS REMOVED FROM SAID PHASE-INVERTING MEANS SAID FIRST SILICON-CONTROLLED RECTIFIER WILL NO LONGER CONDUCT AT THE BEGINNING OF THE FIRST NEGATIVE HALF-CYCLE THEREAFTER, AT WHICH SAID COINCIDENCE IS NOT PRESENT, AND SAID SECONE SILICON-CONTROLLED RECTIFIER WILL NO LONGER CONDUCT AT THE BEGINNING OF THE FIRST POSITIVE HALF-CYCLE THEREAFTER, AT WHICH SAID COINCIDENCE IS NOT PRESENT, THEREBY REMOVING SAID ALTERNATING CURRENT FROM SAID LOAD, SAID APPLICATION OF SAID ALTERNATING CURRENT THEREBY TO SAID LOAD OCCURRING ON THE RISE OF A POSITIVE OR NEGATIVE HALF-CYCLE WITHOUT SUDDEN CHANGE AND THE REMOVAL OF SAID ALTERNATING CURRENT FROM SAID LOAD OCCURRING ON THE FALL OF A HLF-CYCLE WITHOUT SUDDEN CHANGE, SO AS TO ELIMINATE HIGH-FREQUENCY INTERFERENCE PRODUCING TRANSIENTS. 